Earlier this week, a group of 10 militants armed with guns and grenades entered Karachi's Jinnah international airport, where they killed 28 people and themselves. Reports suggest they managed to get past security because the airport continues to use a bomb detector exposed as a fraud in 2010.

The so-called bomb detector, the "ADE 651," is the creation of British con artist James McCormick, who sold more than 6,000 of the devices to Iraqi officials before he was arrested and later sentenced to 10 years in prison. The ADE 651 is little more than an antenna attached by a hinge to a plastic handgrip. When properly used by security personnel — who would be trained to sensitize it to the "molecular frequency" of explosives — the device was supposed to locate bombs by swinging towards them.

If you think this sounds strangely familiar to a divining rod, then you're 100% correct. It operates according to the same principle — the unconscious movements by the operator, known as the ideomotor effect.

Despite McCormick's conviction, the ADE 651 and several variations are still found popping up in hotspots around the world, either as knock-offs of McCormick's invention or distributed by gullible sellers trying to recover their losses. One version of it popped up in Egypt earlier this year, when the country claimed its military experts had invented a device for detecting and curing AIDS and Hepatitis.

Like dowsers, though, many security personnel continued to keep the faith. In 2010, even after McCormick had been charged with fraud, Pakistan's Airport Security Force admitted to the Dawn newspaper that they were continuing to use a device of their own design that operates on the same principle.

Iraq, which had been McCormick's largest market, still uses them too, despite repeated warnings. In 2009, the New York Times confronted bomb squad commander Major General Jehad al-Jabiri with evidence of the ADE 651's fraudulence, yet he insisted that it was effective, saying: "Whether it's magic or scientific, what I care about is it detects bombs." In 2011, al-Jabiri was charged and later jailed for – of all things – taking bribes from McCormick. And still the ADE 651s were being used, as recently October 2013.

At the same time it was apparently common to find Beirut security guards still scanning cars for explosives with an ADE 651, or something similar. And there are reports of other devices being used in the south of Thailand. Indeed, according to Detective Sergeant Steve Mapp, who led the investigation into McCormick, some people's belief in the ADE 651 is almost unshakeable. As he told Business Week, "In Kenya they said, 'No, we know about Mr. McCormick's conviction, but we're really glad we've got them – and they do work.'"